Afibrinogenemia or hypofibrinogenemia is a quantitative defect in fibrinogen. It is a rare disease with estimated frequency of 1 in 1,000,000 population. Routine preoperative screening tests of coagulation disorders are insufficient to detect subtle disorders of fibrinogen. Herein, we report a child who was supposed to undergo open cardiac surgery for a large atrial septal defect. Preoperative coagulation screening tests revealed minimal prolongation of prothrombin time which made us do further work-up. Finally, she was diagnosed with hypofibrinogenemia who was suggested to be congenital.